1. Field of the Invention
The present invention relates to an image forming apparatus such as an electrophotographic copying machine, printer, or facsimile apparatus integrating a post-processing apparatus for paper sheets on which images have been formed.
2. Description of the Prior Art
A processing apparatus is known, which is designed to saddle-stitch image-bearing paper sheets stacked on a proper member by driving metal staples using a stapler constituted by a staple driving means (stitcher) and staple receiving means (clincher) and then discharge the sheet bundle in the form of a two-folded booklet outside the apparatus.
For example, the following arrangement is known as part of a bookbinding apparatus (see, for example, paragraph numbers 0005, 0007, and 0025 and FIGS. 8, 9, and 13 in Japanese Unexamined Patent Publication No. 11-237358 as patent reference 1). A plurality of feeders are provided along the longitudinal direction of a convey means called a gathering chain. Creased paper sheets are stacked on the respective feeders in advance. The paper sheets are then made to fall from the feeders one by one in synchronism with the rotation of the gathering chain so as to be stacked on the chain. Thereafter, a stapler is actuated to wire-stitch the paper sheets.
In another post-processing apparatus, after paper sheets on which images are formed by a printer or the like are stacked on each other at a predetermined position and saddle-stitched by a stapler, the sheet bundle is folded in two in another place and discharged in the form of a booklet (see, for example, paragraph numbers 0027 and 0028 and FIG. 1 in Japanese Unexamined Patent Publication No. 2000-72320 as patent reference 2).
There is known a copying machine, which has a bookbinding function of center-folding paper sheets having undergone copying operation one by one at a middle portion, stacking the paper sheets on an angular support member, and binding the crease portions by using a binding unit (see, for example, the upper right column and FIGS. 2, 3, and 6 in Japanese Unexamined Patent Publication No. 60-254165 as patent reference 3).
In addition, the following automatic online section finishing apparatus is known (see, for example, paragraph numbers 0020 to 0031 and FIGS. 4 to 13 in Japanese Unexamined Patent Publication No. 7-179262 as patent reference 4). In the apparatus, image-bearing paper sheets are creased one by one on a convey path and made to fall on an angular stack means so as to be stacked thereon. The stacked paper sheets are slid on the stack means to be placed at a stapler position to be saddle-stitched. The saddle-stitched sheet bundle is returned to the initial position (middle portion). The sheet bundle is pushed upward by a blade member through the crease of the paper sheet at the lowest position and conveyed to the next process by a pair of rollers functioning as a center-folding means.
According to arrangement disclosed in patent reference 1, however, the necessity of installing a plurality of feeders along the longitudinal direction of the gathering chain will increase the size of the apparatus. In addition, since the sections of paper sheets are made to synchronously fall, it is difficult to perform alignment control. Furthermore, each feeder has a complicated structure.
In addition, since stapling processing (binding process) is performed while the sections of paper sheets are placed on the chain, it is difficult to drive staples at positions on the crease line. As a consequence, the resultant sheet bundle does not look good as a booklet.
The arrangement disclosed in patent reference 2 is designed to perform a center folding process as saddle stitching. Assume that the number of paper sheets is as large as 15 or 20. In this case, although paper sheets located inward can be creased, it becomes more difficult to crease paper sheets located outward due to the lack of power of a center-folding means. When the paper sheets are folded in two to form it into a booklet, therefore, outer paper sheets curl, making it difficult to obtain a booklet in a high quality state.
In other words, even if this apparatus has the ability of the saddle stitching means (to be also referred to as a stapler hereinafter) for binding 20 paper sheets, it is impossible to make the full use of the ability.
In order to make the full use of the ability of the stapler, the size of the arrangement must be increased to increase the power of the center folding means.
In addition, since the saddle stitching unit and center folding unit are arranged at different positions, the production efficiency is not so high.
According to the arrangement disclosed in patent reference 3, creased paper sheets are sequentially stacked on the flat guide plates provided on the two sides of the support member and aligned (position-regulated) by alignment rollers. Thereafter, the two guide plates are pivoted to form an angular shape so as to align the crease of each paper sheet with the top portion of the support member. However, since the mechanism for aligning paper sheets with each other is complicated and has many movable members, it takes much time to support a loose sheet bundle on the support member.
The arrangement disclosed in patent reference 4 needs to apply a load on the paper sheets stacked on the stack means because they are moved when saddle-stitched or to have a special member for discharging the saddle-stitched sheet bundle from the stack means, resulting in inefficient use of space.
Furthermore, the top portion of the stack means is located immediately below the folding rollers, and paper sheets are clamped between the folding rollers by using the buckling of the paper sheets to crease them. This arrangement makes the space near the stack portion crowded. In addition, for the sake of sheet alignment, rotatable paddle wheels must be provided on the two outer sides of the angular stack means.